The present invention relates generally to the art of welding power supplies. More specifically, it relates to the control and/or calibration of welding power supplies.
There are many known welding power supplies used for a variety of welding processes. Welding power supply or system for welding, as used herein, includes one or more of the following components: a wire feeder, a power source or source of power, a torch or gun, a controller, including a wire feeder controller, and a power source controller to control the various components (it may also exclude some of these components). The components may share a housing, or be in separate housings.
Power source, or source of power, as used herein, includes the power circuitry such as rectifiers, switches, transformers, SCRs, etc that process and provide the output power. Controller, as used herein, includes digital and analog circuitry, discrete or integrated circuitry, microprocessors, DSPs, etc., software, hardware and firmware, located on one or more boards, and used to control a welding process, or a device such as a power source or wire feeder.
The components of a welding power supply cooperate to produce a welding output. Generally, the controller controls the other components such that the output parameters (welding current and/or voltage, wire feed speed, etc.) are at a desired level, either set by the user or set by the power supply for the type of process being used.
There are numerous control schemes currently being used. Typically, a control scheme includes receiving feedback, and controlling a command signal in response to that feedback. Feedback, as used herein, includes a signal indicative of or responsive to an output or intermediate signal, which is provided to the controller and control decisions are made in response thereto. Responsive to a parameter, as used herein, includes responding to changes in a value of the parameter or a function of that parameter, such as changing the value of a control signal or other parameter, opening or closing a switch, etc.
Prior art controllers use any number of well known control schemes, such as PID control, comparing a feedback signal to a threshold, open loop control, etc. An example of a prior art control scheme is the control scheme in the MM250(copyright). That control is particularly well suited for MIG welding.
The MM250(copyright) controller receives two user-selectable inputs, one indicating desired welding voltage, and the other desired wire feed speed. User-selectable, as used herein, includes the user setting an operating parameter set point. The controller also receives feedback of these parameters, and compares the set points to the fedback back values. The difference between the set point and the fedback value, or difference error, is integrated over time, and used to change commands such that the output tends to the set point.
One welding process is a short-arc process (and is performed particularly well by the MM250(copyright) power supply). The process has an arc phase, in which the wire advances to the puddle faster than it is melted by the arc. Eventually it reaches the puddle, and the process enters the short phase. Current flow increases in this phase, until it causes a molten metal bridge between the weld puddle and the wire to be broken. This causes the short to be opened, and the process returns to the arc phase. The process alternates between the short and arc phases many times each second.
Prior art short arc-welding systems use voltage control in order to maintain a relatively constant average arc length during welding. This may consist of an open loop system in a constant voltage tapped transformer machine or a voltage control loop. Control loop, open or closed, as used herein, includes a portion of a controller that controls in response to the value of a particular variable.
A prior art voltage control loop filters voltage feedback and compares it to a user-selected voltage set point. The difference, or error, between the set point and actual voltage will result in an adjustment of the output of the welder in the appropriate direction to bring the actual arc voltage closer to the set point.
The amount of filtering of the voltage feedback signal, (or alternately, the error) affects response time and stability. Response time, as used herein, includes the time it takes for a control loop to change the control output in response to changes in a fed back variable. If the filtering is excessive, the response time will be slow, and the output of the machine will not be able to respond to changes in arc length quickly enough and the process may become unstable. If the response time is too short, the intrinsic stability of the periodic molten puddle oscillations may be perturbed and the characteristic regular audible feedback from the process (a.k.a. xe2x80x98the buzzxe2x80x99) can be compromised.
The prior art has suggested that the variable eta may be useful in controlling the welding process. Eta, as used herein, is Tsht/(Tsht+Tarc), where Tsht is the length of time of a short circuit and Tarc is the length of time of the successive arc. Some prior art literature suggests that the MIG welding process will be more stable when eta has a value between 0.2 and 0.3. However, prior art control schemes, particularly those used for CV output, do not generally monitor eta, much less control in response to it.
Accordingly, a welding power supply that provides a fast response, yet avoids instability, is desirable. Additionally, a welding power supply that determines eta, and controls in response to eta, is desirable.
Another welding process (which may be used with or without short arc welding) is a fast-tack process. Fast-tack process, as used herein, includes a welding process consisting of successive short-duration arcs or welds, typically separated by trigger releases and re-triggering at a new location, or at the same location, whereby the process is a start and stop welding process. Such a process is often used to tack weld two components prior to a more complete welding or bonding of them. Arc, as used herein, includes a single arc or a number of sequential arcs, such as those in a fast-tack process
MIG welding may be described as four fundamental sequential states: wait, run-in, weld, and burnback. During the wait state the controller is waiting for a gun or torch trigger, which signals the users intent to weld. The transition to run-in begins when the trigger signal is received. During the run-in state the wire begins to move toward the base metal and the power source produces open circuit voltage. The transition to the weld state occurs when current is detected (indicating an arc or short has been established). During the weld state the wire feeds at a constant speed, and the power source is regulated at a constant voltage in order to maintain a steady arc length. The transition to burnback begins when the trigger signal indicates the trigger has been released. During the burnback state the wire feed motor brakes to stop the wire as quickly as possible, and the power source maintains a constant voltage. As the wire feeder is braking, and the wire feed speed is decreasing, the output voltage ensures that the wire will not stick into the freezing weld pool on the base metal. The transition back to the wait state occurs when a burnback timer expires. These states repeat with the next weld.
Some prior art systems used for fast-tack welding allow the operator to set the desired voltage and wire feed speed for the weld state. However, other parameters such as: wire feed speed during run-in; ramp to run-in wire feed speed (an acceleration parameter which determines how quickly the run-in wire feed speed is achieved); ramp to weld wire feed speed (an acceleration parameter which determines how quickly the weld wire feed speed is achieved); open circuit voltage (the output voltage from the power source during run-in); and burnback voltage (the output voltage from the power source during burnback) affect the welding process.
These parameters (called auxiliary parameters) may be optimized to achieve a good start and stop for each weld. However, the values that optimize a particular start and stop depend on the condition (heat) of the base material and wirexe2x80x94and thus are different for fast-tack welds than for other welds.
Prior art controllers do not provide for user adjustment of the auxiliary parameters, and they are based on the user-set weld voltage and the user set wire feed speed settings. Unfortunately, because welding power supplies are usually used for more than one process, the auxiliary parameters are not optimized for fast-tack welding, but rather for more typical welding processes (or set to a mid range that is perhaps adequate, but not optimal for many processes).
Accordingly, a welding system with a controller that senses when a fast-tack process is being used, and adjusts parameters in response thereto is desirable.
Some prior art welding applications set the run-in wire feed speed and the weld wire feed speed using two separate potentiometers on the welding power supply control panel. One potentiometer is used to set the welding wire feed speed and the other potentiometer is used to set the run-in wire feed speed. Both settings are typically in inches per minute, and each setting is independent of the other. This control scheme is simple and easy to implement. However, the operator must change two potentiometers in order to maintain the same ratio between the two settings.
Another prior art wire feed controller uses a single potentiometer to set both weld wire feed speed and run-in wire feed speed. A microcontroller (also called microprocesor) in the wire feed speed control interprets the position of the control knob as indicating run-in wire feed speed under certain conditionsxe2x80x94when power is applied to the machine and the trigger is engaged, e.g.
According to an algorithm initiated when power is applied to the machine and the trigger is engaged, if the control potentiometer is fully counter clockwise, a run-in wire feed speed of 50 IPM is registered. If the control potentiometer is fully clockwise, the run-in wire feed speed is the same as the weld wire feed speed. The position of the knob when the trigger is engaged other than at start-up indicates the weld wire feed speed. This control is more difficult to implement, and the run-in wire feed speed is independent of the weld wire feed speed and the ratio of run-in to weld wire feed speed changes when the operator changes the weld wire feed speed.
Accordingly, a weld wire feed speed setting that is set as a percentage of weld wire feed speed is desirable. It will preferably use a single potentiometer.
Any control scheme needs accurately scaled inputs and outputs (commands) to accurately control a welding process. Prior art welding power supplies scale the inputs and outputs by calibrating the control board, to compensate for tolerances in the components used.
Typically, potentiometers on the control board are adjusted at the manufacturer. One calibration technique is to adjust the front panel potentiometer (user-selectable input) to a minimum value. Then, the output is measured and a control board potentiometer is adjusted until the output is the desired minimum output. For example, if the machine minimum output load voltage is supposed to be 14 volts, then the user-adjustable potentiometer on the front panel is set to the minimum. If the measured output load voltage is 15 volts, the control board calibration potentiometer is adjusted to lower the output voltage to 14 volts.
The process is repeated for the desired maximum output load voltage. Using two calibration potentiometers results in a slope calibration (the adjusted value is determined by a line equation). Other calibrations use two points other than the max and min, such as the max and mid-range. The control board calibration potentiometers may scale the feedback inputs, or the command outputs. In addition to load voltage, wire feed speed is also calibrated.
This calibration scheme is easy to implement, however the tolerance and drift in the potentiometer used for calibration adds to the total error tolerance of the system. Also, the initial setting of a potentiometer is unknown and it is often desirable to have a baseline, or starting point.
Accordingly, a welding power supply that may be calibrated such that the calibration does not drift and add to the system error is desirable. Preferably, it will be able to store the calibration values, and be able to provide them to the user.
According to a first aspect of the invention a system for welding includes a welding-type power source, a feedback circuit and a controller. The power source has at least one control input and a welding-type output. The feedback circuit is responsive to the welding-type output and has a feedback output. The controller has a feedback input connected to the feedback output, an eta control circuit responsive to the feedback input, and an eta output. It also has at least one control loop having a selectable response time, and a response time selector responsive to the eta output. A control output is connected to the control input.
According to a second aspect of the invention a system for welding includes a welding-type power supply that has at least one control input and a welding-type output. A feedback circuit is responsive to the welding-type output, and has a feedback output. A controller has a feedback input connected to the feedback output of the feedback circuit, a voltage control loop responsive to the feedback input, and a temporal control loop responsive to the feedback input. It has a control output, responsive to that voltage control loop and the temporal control loop, connected to the control input.
According to a third aspect of the invention a welding-type power supply controller includes at least one feedback input, a voltage control loop, and an eta controller. The voltage control loop includes a voltage feedback input connected to the feedback input, and an integrator with first and second feedback capacitors. A switch, with a switch control input, is in series with the second capacitor. The eta controller has an input connected to the feedback input and an output connected to the switch control input.
According to a fifth aspect of the invention a method of providing welding power includes providing a welding-type power output, feeding back a parameter of the power output and controlling the welding-type power in response to the feeding back using a voltage control loop and a temporal control loop.
According to a sixth aspect of the invention a method of controlling welding-type power includes providing voltage feedback, integrating the difference between a voltage feedback and a threshold using an integrator with first and second capacitors in a feedback path, comparing eta to a window, and switching the second feedback capacitor in and out of the feedback path in response to comparing eta.
The control loop has at least two response times, or a plurality of response times chosen from a range of response times in various embodiments.
The power source is an SCR based, phase controlled, power source and/or the controller is a microprocessor controller in other embodiments.
The feedback circuit includes a voltage feedback circuit, the response time selector includes an integrator responsive to an eta window, and/or the control loop includes a voltage control loop and a temporal control loop in alternative embodiments.
According to a seventh aspect of the invention a method of providing welding power includes providing a welding-type output, and feeding back an output parameter. Eta is determined, and the welding-type output is controlled in response to the feeding back. A response time is selected in response to eta.
According to an eighth aspect of the invention a system for welding includes a welding power source, a wire feeder, a feedback circuit, and a controller. The power source has at least one power source control input and a welding power output. The wire feeder is connected to the welding power output and has a wire feed speed input. The feedback circuit is responsive to the welding power output, and has a feedback output. The controller has a feedback input connected to the feedback output and a fast-tack detect circuit responsive to a trigger signal. It also has a speed control output responsive to the fast-tack detect circuit, and in electrical communication with the wire feed speed input, and a power source control output responsive to the fast-tack detect circuit, and in electrical communication with power source control input.
According to another aspect of the invention a method of welding includes supplying welding power to an arc, feeding wire to the arc, feeding back a signal responsive to the welding power, detecting whether or not the process is a fast-tack process, controlling the supply of power according to a first control scheme if the process is a fast-tack process, and controlling the supply of power according to a second control scheme if the process is not a fast-tack process.
A fast-tack control circuit is disposed electrically between the fast-tack detect circuit and the power source control output, and disposed electrically between the fast-tack detect circuit and the wire-feed speed output and a weld control circuit is disposed electrically between the fast-tack detect circuit and the power source control output and disposed electrically between the fast-tack detect circuit and the wire-feed speed output in one alternative.
The power source control output includes a voltage command, including at least one of an open circuit command and a burn back command, and the wire feed speed output includes a ramp to run-in command, and/or the fast-tack detect circuit includes a timer circuit responsive to a trigger signal in other embodiments.
An inductor winding is in electrical communication with the welding power output and an auxiliary winding is in magnetic and electrical communication with the inductor winding. A switch circuit is in series with the auxiliary winding, and the switch circuit is responsive to the fast-tack detect circuit in another embodiment.
According to yet another aspect of the invention a system for welding includes a welding power source, a wire feeder and a controller. The welding power source has a welding power output connected to the wire feeder. The wire feeder has a speed control input connected to a speed control output of the controller. The speed control output has a weld wire speed set point, and a run-in wire speed set point. The run-in speed set point is a set percentage of the weld wire speed set point.
Another aspect of the invention is a method of welding that includes providing welding power to an arc, feeding wire to the arc, controlling the speed of the wire during a run-in state, and controlling the speed of the wire during a weld state. The run-in speed set is a set percentage of the weld speed.
The set percentage is a user selectable percentage, and/or between 25 percent and 150 percent in various alternatives.
The percentage is set using the weld wire feed speed input, and an enable signal in another alternative.
According to yet another aspect of the invention a welding-type power supply includes a power source, a controller, and a user-selectable input, such as a potentiometer. The controller is connected to the power source, and has at least one set point input, and at least one calibration input. The user-selectable input is connected to the at least one set point input, and connected to at the least-one calibration input.
According to another aspect of the invention a method of calibrating a welding-type power supply, of the type having a user-selectable set point input, includes detecting whether or not the power supply is in a calibration mode, receiving a value from the user-selectable set point input as a calibration value if the power supply is in the calibration mode, and receiving a value from the user-selectable set point input as a set point value if the power supply is not in the calibration mode.
An input-selection circuit, connected to the controller, enables one of the calibration input and set point input, and disables the other of the set point input and calibration input. A user-selectable switch, such as a toggle switch, is connected to the input-selection circuit in other embodiments
The controller is a microprocessor controller, and stores at least one user-selected calibration value received on the calibration input in another embodiment.
Other principal features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description and the appended claims.